1 //===- RegAllocBase.cpp - Register Allocator Base Class -------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file defines the RegAllocBase class which provides common functionality
10 // for LiveIntervalUnion-based register allocators.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #include "RegAllocBase.h"
15 #include "llvm/ADT/SmallVector.h"
16 #include "llvm/ADT/Statistic.h"
17 #include "llvm/CodeGen/LiveInterval.h"
18 #include "llvm/CodeGen/LiveIntervals.h"
19 #include "llvm/CodeGen/LiveRegMatrix.h"
20 #include "llvm/CodeGen/MachineInstr.h"
21 #include "llvm/CodeGen/MachineModuleInfo.h"
22 #include "llvm/CodeGen/MachineRegisterInfo.h"
23 #include "llvm/CodeGen/Spiller.h"
24 #include "llvm/CodeGen/TargetRegisterInfo.h"
25 #include "llvm/CodeGen/VirtRegMap.h"
26 #include "llvm/Pass.h"
27 #include "llvm/Support/CommandLine.h"
28 #include "llvm/Support/Debug.h"
29 #include "llvm/Support/ErrorHandling.h"
30 #include "llvm/Support/Timer.h"
31 #include "llvm/Support/raw_ostream.h"
32 #include <cassert>
33
34 using namespace llvm;
35
36 #define DEBUG_TYPE "regalloc"
37
38 STATISTIC(NumNewQueued , "Number of new live ranges queued");
39
40 // Temporary verification option until we can put verification inside
41 // MachineVerifier.
42 static cl::opt<bool, true>
43 VerifyRegAlloc("verify-regalloc", cl::location(RegAllocBase::VerifyEnabled),
44 cl::Hidden, cl::desc("Verify during register allocation"));
45
46 const char RegAllocBase::TimerGroupName[] = "regalloc";
47 const char RegAllocBase::TimerGroupDescription[] = "Register Allocation";
48 bool RegAllocBase::VerifyEnabled = false;
49
50 //===----------------------------------------------------------------------===//
51 // RegAllocBase Implementation
52 //===----------------------------------------------------------------------===//
53
54 // Pin the vtable to this file.
anchor()55 void RegAllocBase::anchor() {}
56
init(VirtRegMap & vrm,LiveIntervals & lis,LiveRegMatrix & mat)57 void RegAllocBase::init(VirtRegMap &vrm,
58 LiveIntervals &lis,
59 LiveRegMatrix &mat) {
60 TRI = &vrm.getTargetRegInfo();
61 MRI = &vrm.getRegInfo();
62 VRM = &vrm;
63 LIS = &lis;
64 Matrix = &mat;
65 MRI->freezeReservedRegs(vrm.getMachineFunction());
66 RegClassInfo.runOnMachineFunction(vrm.getMachineFunction());
67 }
68
69 // Visit all the live registers. If they are already assigned to a physical
70 // register, unify them with the corresponding LiveIntervalUnion, otherwise push
71 // them on the priority queue for later assignment.
seedLiveRegs()72 void RegAllocBase::seedLiveRegs() {
73 NamedRegionTimer T("seed", "Seed Live Regs", TimerGroupName,
74 TimerGroupDescription, TimePassesIsEnabled);
75 for (unsigned i = 0, e = MRI->getNumVirtRegs(); i != e; ++i) {
76 Register Reg = Register::index2VirtReg(i);
77 if (MRI->reg_nodbg_empty(Reg))
78 continue;
79 enqueue(&LIS->getInterval(Reg));
80 }
81 }
82
83 // Top-level driver to manage the queue of unassigned VirtRegs and call the
84 // selectOrSplit implementation.
allocatePhysRegs()85 void RegAllocBase::allocatePhysRegs() {
86 seedLiveRegs();
87
88 // Continue assigning vregs one at a time to available physical registers.
89 while (LiveInterval *VirtReg = dequeue()) {
90 assert(!VRM->hasPhys(VirtReg->reg()) && "Register already assigned");
91
92 // Unused registers can appear when the spiller coalesces snippets.
93 if (MRI->reg_nodbg_empty(VirtReg->reg())) {
94 LLVM_DEBUG(dbgs() << "Dropping unused " << *VirtReg << '\n');
95 aboutToRemoveInterval(*VirtReg);
96 LIS->removeInterval(VirtReg->reg());
97 continue;
98 }
99
100 // Invalidate all interference queries, live ranges could have changed.
101 Matrix->invalidateVirtRegs();
102
103 // selectOrSplit requests the allocator to return an available physical
104 // register if possible and populate a list of new live intervals that
105 // result from splitting.
106 LLVM_DEBUG(dbgs() << "\nselectOrSplit "
107 << TRI->getRegClassName(MRI->getRegClass(VirtReg->reg()))
108 << ':' << *VirtReg << " w=" << VirtReg->weight() << '\n');
109
110 using VirtRegVec = SmallVector<Register, 4>;
111
112 VirtRegVec SplitVRegs;
113 MCRegister AvailablePhysReg = selectOrSplit(*VirtReg, SplitVRegs);
114
115 if (AvailablePhysReg == ~0u) {
116 // selectOrSplit failed to find a register!
117 // Probably caused by an inline asm.
118 MachineInstr *MI = nullptr;
119 for (MachineRegisterInfo::reg_instr_iterator
120 I = MRI->reg_instr_begin(VirtReg->reg()),
121 E = MRI->reg_instr_end();
122 I != E;) {
123 MI = &*(I++);
124 if (MI->isInlineAsm())
125 break;
126 }
127 if (MI && MI->isInlineAsm()) {
128 MI->emitError("inline assembly requires more registers than available");
129 } else if (MI) {
130 LLVMContext &Context =
131 MI->getParent()->getParent()->getMMI().getModule()->getContext();
132 Context.emitError("ran out of registers during register allocation");
133 } else {
134 report_fatal_error("ran out of registers during register allocation");
135 }
136 // Keep going after reporting the error.
137 VRM->assignVirt2Phys(
138 VirtReg->reg(),
139 RegClassInfo.getOrder(MRI->getRegClass(VirtReg->reg())).front());
140 continue;
141 }
142
143 if (AvailablePhysReg)
144 Matrix->assign(*VirtReg, AvailablePhysReg);
145
146 for (Register Reg : SplitVRegs) {
147 assert(LIS->hasInterval(Reg));
148
149 LiveInterval *SplitVirtReg = &LIS->getInterval(Reg);
150 assert(!VRM->hasPhys(SplitVirtReg->reg()) && "Register already assigned");
151 if (MRI->reg_nodbg_empty(SplitVirtReg->reg())) {
152 assert(SplitVirtReg->empty() && "Non-empty but used interval");
153 LLVM_DEBUG(dbgs() << "not queueing unused " << *SplitVirtReg << '\n');
154 aboutToRemoveInterval(*SplitVirtReg);
155 LIS->removeInterval(SplitVirtReg->reg());
156 continue;
157 }
158 LLVM_DEBUG(dbgs() << "queuing new interval: " << *SplitVirtReg << "\n");
159 assert(Register::isVirtualRegister(SplitVirtReg->reg()) &&
160 "expect split value in virtual register");
161 enqueue(SplitVirtReg);
162 ++NumNewQueued;
163 }
164 }
165 }
166
postOptimization()167 void RegAllocBase::postOptimization() {
168 spiller().postOptimization();
169 for (auto DeadInst : DeadRemats) {
170 LIS->RemoveMachineInstrFromMaps(*DeadInst);
171 DeadInst->eraseFromParent();
172 }
173 DeadRemats.clear();
174 }
175